This is the most severe form of allergic reaction. It can develop in minutes or even seconds after contact with an allergen, or it may appear half an hour or more later, or even progress suddenly from an apparently mild allergic reaction.
The face, chest and back may become flushed, itchy and burning. The face, tongue and lips may swell and the lips turn blue. Breathing becomes difficult and noisy. The pulse becomes weak and rapid. Pale skin, dizziness, nausea and headache may follow. Finally, in very serious cases, the person may faint and lapse into a coma.
The person needs immediate medical assistance. Treat for shock and ensure that he has an open airway. If he becomes unconscious, place him in the recovery position. If breathing fails, start artificial respiration immediately. Take him to a doctor or call an ambulance.